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1 | /* |
1 | /* |
2 | * Copyright (C) 2001-2004 Jakub Jermar |
2 | * Copyright (C) 2001-2004 Jakub Jermar |
3 | * All rights reserved. |
3 | * All rights reserved. |
4 | * |
4 | * |
5 | * Redistribution and use in source and binary forms, with or without |
5 | * Redistribution and use in source and binary forms, with or without |
6 | * modification, are permitted provided that the following conditions |
6 | * modification, are permitted provided that the following conditions |
7 | * are met: |
7 | * are met: |
8 | * |
8 | * |
9 | * - Redistributions of source code must retain the above copyright |
9 | * - Redistributions of source code must retain the above copyright |
10 | * notice, this list of conditions and the following disclaimer. |
10 | * notice, this list of conditions and the following disclaimer. |
11 | * - Redistributions in binary form must reproduce the above copyright |
11 | * - Redistributions in binary form must reproduce the above copyright |
12 | * notice, this list of conditions and the following disclaimer in the |
12 | * notice, this list of conditions and the following disclaimer in the |
13 | * documentation and/or other materials provided with the distribution. |
13 | * documentation and/or other materials provided with the distribution. |
14 | * - The name of the author may not be used to endorse or promote products |
14 | * - The name of the author may not be used to endorse or promote products |
15 | * derived from this software without specific prior written permission. |
15 | * derived from this software without specific prior written permission. |
16 | * |
16 | * |
17 | * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR |
17 | * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR |
18 | * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES |
18 | * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES |
19 | * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. |
19 | * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. |
20 | * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, |
20 | * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, |
21 | * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT |
21 | * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT |
22 | * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
22 | * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
23 | * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
23 | * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
24 | * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
24 | * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
25 | * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF |
25 | * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF |
26 | * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
26 | * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
27 | */ |
27 | */ |
28 | 28 | ||
29 | /** |
29 | /** |
30 | * @file rwlock.c |
30 | * @file rwlock.c |
31 | * @brief Reader/Writer locks. |
31 | * @brief Reader/Writer locks. |
32 | * |
32 | * |
33 | * A reader/writer lock can be held by multiple readers at a time. |
33 | * A reader/writer lock can be held by multiple readers at a time. |
34 | * Or it can be exclusively held by a sole writer at a time. |
34 | * Or it can be exclusively held by a sole writer at a time. |
35 | * |
35 | * |
36 | * These locks are not recursive. |
36 | * These locks are not recursive. |
37 | * Because technique called direct hand-off is used, neither readers |
37 | * Because technique called direct hand-off is used, neither readers |
38 | * nor writers will suffer starvation. |
38 | * nor writers will suffer starvation. |
39 | * |
39 | * |
40 | * If there is a writer followed by a reader waiting for the rwlock |
40 | * If there is a writer followed by a reader waiting for the rwlock |
41 | * and the writer times out, all leading readers are automatically woken up |
41 | * and the writer times out, all leading readers are automatically woken up |
42 | * and allowed in. |
42 | * and allowed in. |
43 | */ |
43 | */ |
44 | 44 | ||
45 | /* |
45 | /* |
46 | * NOTE ON rwlock_holder_type |
46 | * NOTE ON rwlock_holder_type |
47 | * This field is set on an attempt to acquire the exclusive mutex |
47 | * This field is set on an attempt to acquire the exclusive mutex |
48 | * to the respective value depending whether the caller is a reader |
48 | * to the respective value depending whether the caller is a reader |
49 | * or a writer. The field is examined only if the thread had been |
49 | * or a writer. The field is examined only if the thread had been |
50 | * previously blocked on the exclusive mutex. Thus it is save |
50 | * previously blocked on the exclusive mutex. Thus it is save |
51 | * to store the rwlock type in the thread structure, because |
51 | * to store the rwlock type in the thread structure, because |
52 | * each thread can block on only one rwlock at a time. |
52 | * each thread can block on only one rwlock at a time. |
53 | */ |
53 | */ |
54 | 54 | ||
55 | #include <synch/rwlock.h> |
55 | #include <synch/rwlock.h> |
56 | #include <synch/spinlock.h> |
56 | #include <synch/spinlock.h> |
57 | #include <synch/mutex.h> |
57 | #include <synch/mutex.h> |
58 | #include <synch/waitq.h> |
58 | #include <synch/waitq.h> |
59 | #include <synch/synch.h> |
59 | #include <synch/synch.h> |
60 | #include <adt/list.h> |
60 | #include <adt/list.h> |
61 | #include <typedefs.h> |
61 | #include <typedefs.h> |
62 | #include <arch/asm.h> |
62 | #include <arch/asm.h> |
63 | #include <arch.h> |
63 | #include <arch.h> |
64 | #include <proc/thread.h> |
64 | #include <proc/thread.h> |
65 | #include <panic.h> |
65 | #include <panic.h> |
66 | 66 | ||
67 | #define ALLOW_ALL 0 |
67 | #define ALLOW_ALL 0 |
68 | #define ALLOW_READERS_ONLY 1 |
68 | #define ALLOW_READERS_ONLY 1 |
69 | 69 | ||
70 | static void let_others_in(rwlock_t *rwl, int readers_only); |
70 | static void let_others_in(rwlock_t *rwl, int readers_only); |
71 | static void release_spinlock(void *arg); |
71 | static void release_spinlock(void *arg); |
72 | 72 | ||
73 | /** Initialize reader/writer lock |
73 | /** Initialize reader/writer lock |
74 | * |
74 | * |
75 | * Initialize reader/writer lock. |
75 | * Initialize reader/writer lock. |
76 | * |
76 | * |
77 | * @param rwl Reader/Writer lock. |
77 | * @param rwl Reader/Writer lock. |
78 | */ |
78 | */ |
79 | void rwlock_initialize(rwlock_t *rwl) { |
79 | void rwlock_initialize(rwlock_t *rwl) { |
80 | spinlock_initialize(&rwl->lock, "rwlock_t"); |
80 | spinlock_initialize(&rwl->lock, "rwlock_t"); |
81 | mutex_initialize(&rwl->exclusive); |
81 | mutex_initialize(&rwl->exclusive); |
82 | rwl->readers_in = 0; |
82 | rwl->readers_in = 0; |
83 | } |
83 | } |
84 | 84 | ||
85 | /** Acquire reader/writer lock for reading |
85 | /** Acquire reader/writer lock for reading |
86 | * |
86 | * |
87 | * Acquire reader/writer lock for reading. |
87 | * Acquire reader/writer lock for reading. |
88 | * Timeout and willingness to block may be specified. |
88 | * Timeout and willingness to block may be specified. |
89 | * |
89 | * |
90 | * @param rwl Reader/Writer lock. |
90 | * @param rwl Reader/Writer lock. |
91 | * @param usec Timeout in microseconds. |
91 | * @param usec Timeout in microseconds. |
92 | * @param trylock Switches between blocking and non-blocking mode. |
92 | * @param flags Specify mode of operation. |
93 | * |
93 | * |
94 | * For exact description of possible combinations of |
94 | * For exact description of possible combinations of |
95 | * @usec and @trylock, see comment for waitq_sleep_timeout(). |
95 | * usec and flags, see comment for waitq_sleep_timeout(). |
96 | * |
96 | * |
97 | * @return See comment for waitq_sleep_timeout(). |
97 | * @return See comment for waitq_sleep_timeout(). |
98 | */ |
98 | */ |
99 | int _rwlock_write_lock_timeout(rwlock_t *rwl, __u32 usec, int trylock) |
99 | int _rwlock_write_lock_timeout(rwlock_t *rwl, __u32 usec, int flags) |
100 | { |
100 | { |
101 | ipl_t ipl; |
101 | ipl_t ipl; |
102 | int rc; |
102 | int rc; |
103 | 103 | ||
104 | ipl = interrupts_disable(); |
104 | ipl = interrupts_disable(); |
105 | spinlock_lock(&THREAD->lock); |
105 | spinlock_lock(&THREAD->lock); |
106 | THREAD->rwlock_holder_type = RWLOCK_WRITER; |
106 | THREAD->rwlock_holder_type = RWLOCK_WRITER; |
107 | spinlock_unlock(&THREAD->lock); |
107 | spinlock_unlock(&THREAD->lock); |
108 | interrupts_restore(ipl); |
108 | interrupts_restore(ipl); |
109 | 109 | ||
110 | /* |
110 | /* |
111 | * Writers take the easy part. |
111 | * Writers take the easy part. |
112 | * They just need to acquire the exclusive mutex. |
112 | * They just need to acquire the exclusive mutex. |
113 | */ |
113 | */ |
114 | rc = _mutex_lock_timeout(&rwl->exclusive, usec, trylock); |
114 | rc = _mutex_lock_timeout(&rwl->exclusive, usec, flags); |
115 | if (SYNCH_FAILED(rc)) { |
115 | if (SYNCH_FAILED(rc)) { |
116 | 116 | ||
117 | /* |
117 | /* |
118 | * Lock operation timed out. |
118 | * Lock operation timed out or was interrupted. |
119 | * The state of rwl is UNKNOWN at this point. |
119 | * The state of rwl is UNKNOWN at this point. |
120 | * No claims about its holder can be made. |
120 | * No claims about its holder can be made. |
121 | */ |
121 | */ |
122 | 122 | ||
123 | ipl = interrupts_disable(); |
123 | ipl = interrupts_disable(); |
124 | spinlock_lock(&rwl->lock); |
124 | spinlock_lock(&rwl->lock); |
125 | /* |
125 | /* |
126 | * Now when rwl is locked, we can inspect it again. |
126 | * Now when rwl is locked, we can inspect it again. |
127 | * If it is held by some readers already, we can let |
127 | * If it is held by some readers already, we can let |
128 | * readers from the head of the wait queue in. |
128 | * readers from the head of the wait queue in. |
129 | */ |
129 | */ |
130 | if (rwl->readers_in) |
130 | if (rwl->readers_in) |
131 | let_others_in(rwl, ALLOW_READERS_ONLY); |
131 | let_others_in(rwl, ALLOW_READERS_ONLY); |
132 | spinlock_unlock(&rwl->lock); |
132 | spinlock_unlock(&rwl->lock); |
133 | interrupts_restore(ipl); |
133 | interrupts_restore(ipl); |
134 | } |
134 | } |
135 | 135 | ||
136 | return rc; |
136 | return rc; |
137 | } |
137 | } |
138 | 138 | ||
139 | /** Acquire reader/writer lock for writing |
139 | /** Acquire reader/writer lock for writing |
140 | * |
140 | * |
141 | * Acquire reader/writer lock for writing. |
141 | * Acquire reader/writer lock for writing. |
142 | * Timeout and willingness to block may be specified. |
142 | * Timeout and willingness to block may be specified. |
143 | * |
143 | * |
144 | * @param rwl Reader/Writer lock. |
144 | * @param rwl Reader/Writer lock. |
145 | * @param usec Timeout in microseconds. |
145 | * @param usec Timeout in microseconds. |
146 | * @param trylock Switches between blocking and non-blocking mode. |
146 | * @param flags Select mode of operation. |
147 | * |
147 | * |
148 | * For exact description of possible combinations of |
148 | * For exact description of possible combinations of |
149 | * usec and trylock, see comment for waitq_sleep_timeout(). |
149 | * usec and flags, see comment for waitq_sleep_timeout(). |
150 | * |
150 | * |
151 | * @return See comment for waitq_sleep_timeout(). |
151 | * @return See comment for waitq_sleep_timeout(). |
152 | */ |
152 | */ |
153 | int _rwlock_read_lock_timeout(rwlock_t *rwl, __u32 usec, int trylock) |
153 | int _rwlock_read_lock_timeout(rwlock_t *rwl, __u32 usec, int flags) |
154 | { |
154 | { |
155 | int rc; |
155 | int rc; |
156 | ipl_t ipl; |
156 | ipl_t ipl; |
157 | 157 | ||
158 | ipl = interrupts_disable(); |
158 | ipl = interrupts_disable(); |
159 | spinlock_lock(&THREAD->lock); |
159 | spinlock_lock(&THREAD->lock); |
160 | THREAD->rwlock_holder_type = RWLOCK_READER; |
160 | THREAD->rwlock_holder_type = RWLOCK_READER; |
161 | spinlock_unlock(&THREAD->lock); |
161 | spinlock_unlock(&THREAD->lock); |
162 | 162 | ||
163 | spinlock_lock(&rwl->lock); |
163 | spinlock_lock(&rwl->lock); |
164 | 164 | ||
165 | /* |
165 | /* |
166 | * Find out whether we can get what we want without blocking. |
166 | * Find out whether we can get what we want without blocking. |
167 | */ |
167 | */ |
168 | rc = mutex_trylock(&rwl->exclusive); |
168 | rc = mutex_trylock(&rwl->exclusive); |
169 | if (SYNCH_FAILED(rc)) { |
169 | if (SYNCH_FAILED(rc)) { |
170 | 170 | ||
171 | /* |
171 | /* |
172 | * 'exclusive' mutex is being held by someone else. |
172 | * 'exclusive' mutex is being held by someone else. |
173 | * If the holder is a reader and there is no one |
173 | * If the holder is a reader and there is no one |
174 | * else waiting for it, we can enter the critical |
174 | * else waiting for it, we can enter the critical |
175 | * section. |
175 | * section. |
176 | */ |
176 | */ |
177 | 177 | ||
178 | if (rwl->readers_in) { |
178 | if (rwl->readers_in) { |
179 | spinlock_lock(&rwl->exclusive.sem.wq.lock); |
179 | spinlock_lock(&rwl->exclusive.sem.wq.lock); |
180 | if (list_empty(&rwl->exclusive.sem.wq.head)) { |
180 | if (list_empty(&rwl->exclusive.sem.wq.head)) { |
181 | /* |
181 | /* |
182 | * We can enter. |
182 | * We can enter. |
183 | */ |
183 | */ |
184 | spinlock_unlock(&rwl->exclusive.sem.wq.lock); |
184 | spinlock_unlock(&rwl->exclusive.sem.wq.lock); |
185 | goto shortcut; |
185 | goto shortcut; |
186 | } |
186 | } |
187 | spinlock_unlock(&rwl->exclusive.sem.wq.lock); |
187 | spinlock_unlock(&rwl->exclusive.sem.wq.lock); |
188 | } |
188 | } |
189 | 189 | ||
190 | /* |
190 | /* |
191 | * In order to prevent a race condition when a reader |
191 | * In order to prevent a race condition when a reader |
192 | * could block another reader at the head of the waitq, |
192 | * could block another reader at the head of the waitq, |
193 | * we register a function to unlock rwl->lock |
193 | * we register a function to unlock rwl->lock |
194 | * after this thread is put asleep. |
194 | * after this thread is put asleep. |
195 | */ |
195 | */ |
196 | #ifdef CONFIG_SMP |
196 | #ifdef CONFIG_SMP |
197 | thread_register_call_me(release_spinlock, &rwl->lock); |
197 | thread_register_call_me(release_spinlock, &rwl->lock); |
198 | #else |
198 | #else |
199 | thread_register_call_me(release_spinlock, NULL); |
199 | thread_register_call_me(release_spinlock, NULL); |
200 | #endif |
200 | #endif |
201 | 201 | ||
202 | rc = _mutex_lock_timeout(&rwl->exclusive, usec, trylock); |
202 | rc = _mutex_lock_timeout(&rwl->exclusive, usec, flags); |
203 | switch (rc) { |
203 | switch (rc) { |
204 | case ESYNCH_WOULD_BLOCK: |
204 | case ESYNCH_WOULD_BLOCK: |
205 | /* |
205 | /* |
206 | * release_spinlock() wasn't called |
206 | * release_spinlock() wasn't called |
207 | */ |
207 | */ |
208 | thread_register_call_me(NULL, NULL); |
208 | thread_register_call_me(NULL, NULL); |
209 | spinlock_unlock(&rwl->lock); |
209 | spinlock_unlock(&rwl->lock); |
210 | case ESYNCH_TIMEOUT: |
210 | case ESYNCH_TIMEOUT: |
- | 211 | case ESYNCH_INTERRUPTED: |
|
211 | /* |
212 | /* |
212 | * The sleep timeouted. |
213 | * The sleep timed out. |
213 | * We just restore interrupt priority level. |
214 | * We just restore interrupt priority level. |
214 | */ |
215 | */ |
215 | case ESYNCH_OK_BLOCKED: |
216 | case ESYNCH_OK_BLOCKED: |
216 | /* |
217 | /* |
217 | * We were woken with rwl->readers_in already incremented. |
218 | * We were woken with rwl->readers_in already incremented. |
218 | * Note that this arrangement avoids race condition between |
219 | * Note that this arrangement avoids race condition between |
219 | * two concurrent readers. (Race is avoided if 'exclusive' is |
220 | * two concurrent readers. (Race is avoided if 'exclusive' is |
220 | * locked at the same time as 'readers_in' is incremented. |
221 | * locked at the same time as 'readers_in' is incremented. |
221 | * Same time means both events happen atomically when |
222 | * Same time means both events happen atomically when |
222 | * rwl->lock is held.) |
223 | * rwl->lock is held.) |
223 | */ |
224 | */ |
224 | interrupts_restore(ipl); |
225 | interrupts_restore(ipl); |
225 | break; |
226 | break; |
226 | case ESYNCH_OK_ATOMIC: |
227 | case ESYNCH_OK_ATOMIC: |
227 | panic("_mutex_lock_timeout()==ESYNCH_OK_ATOMIC\n"); |
228 | panic("_mutex_lock_timeout()==ESYNCH_OK_ATOMIC\n"); |
228 | break; |
229 | break; |
229 | default: |
230 | default: |
230 | panic("invalid ESYNCH\n"); |
231 | panic("invalid ESYNCH\n"); |
231 | break; |
232 | break; |
232 | } |
233 | } |
233 | return rc; |
234 | return rc; |
234 | } |
235 | } |
235 | 236 | ||
236 | shortcut: |
237 | shortcut: |
237 | 238 | ||
238 | /* |
239 | /* |
239 | * We can increment readers_in only if we didn't go to sleep. |
240 | * We can increment readers_in only if we didn't go to sleep. |
240 | * For sleepers, rwlock_let_others_in() will do the job. |
241 | * For sleepers, rwlock_let_others_in() will do the job. |
241 | */ |
242 | */ |
242 | rwl->readers_in++; |
243 | rwl->readers_in++; |
243 | 244 | ||
244 | spinlock_unlock(&rwl->lock); |
245 | spinlock_unlock(&rwl->lock); |
245 | interrupts_restore(ipl); |
246 | interrupts_restore(ipl); |
246 | 247 | ||
247 | return ESYNCH_OK_ATOMIC; |
248 | return ESYNCH_OK_ATOMIC; |
248 | } |
249 | } |
249 | 250 | ||
250 | /** Release reader/writer lock held by writer |
251 | /** Release reader/writer lock held by writer |
251 | * |
252 | * |
252 | * Release reader/writer lock held by writer. |
253 | * Release reader/writer lock held by writer. |
253 | * Handoff reader/writer lock ownership directly |
254 | * Handoff reader/writer lock ownership directly |
254 | * to waiting readers or a writer. |
255 | * to waiting readers or a writer. |
255 | * |
256 | * |
256 | * @param rwl Reader/Writer lock. |
257 | * @param rwl Reader/Writer lock. |
257 | */ |
258 | */ |
258 | void rwlock_write_unlock(rwlock_t *rwl) |
259 | void rwlock_write_unlock(rwlock_t *rwl) |
259 | { |
260 | { |
260 | ipl_t ipl; |
261 | ipl_t ipl; |
261 | 262 | ||
262 | ipl = interrupts_disable(); |
263 | ipl = interrupts_disable(); |
263 | spinlock_lock(&rwl->lock); |
264 | spinlock_lock(&rwl->lock); |
264 | let_others_in(rwl, ALLOW_ALL); |
265 | let_others_in(rwl, ALLOW_ALL); |
265 | spinlock_unlock(&rwl->lock); |
266 | spinlock_unlock(&rwl->lock); |
266 | interrupts_restore(ipl); |
267 | interrupts_restore(ipl); |
267 | 268 | ||
268 | } |
269 | } |
269 | 270 | ||
270 | /** Release reader/writer lock held by reader |
271 | /** Release reader/writer lock held by reader |
271 | * |
272 | * |
272 | * Release reader/writer lock held by reader. |
273 | * Release reader/writer lock held by reader. |
273 | * Handoff reader/writer lock ownership directly |
274 | * Handoff reader/writer lock ownership directly |
274 | * to a waiting writer or don't do anything if more |
275 | * to a waiting writer or don't do anything if more |
275 | * readers poses the lock. |
276 | * readers poses the lock. |
276 | * |
277 | * |
277 | * @param rwl Reader/Writer lock. |
278 | * @param rwl Reader/Writer lock. |
278 | */ |
279 | */ |
279 | void rwlock_read_unlock(rwlock_t *rwl) |
280 | void rwlock_read_unlock(rwlock_t *rwl) |
280 | { |
281 | { |
281 | ipl_t ipl; |
282 | ipl_t ipl; |
282 | 283 | ||
283 | ipl = interrupts_disable(); |
284 | ipl = interrupts_disable(); |
284 | spinlock_lock(&rwl->lock); |
285 | spinlock_lock(&rwl->lock); |
285 | if (!--rwl->readers_in) |
286 | if (!--rwl->readers_in) |
286 | let_others_in(rwl, ALLOW_ALL); |
287 | let_others_in(rwl, ALLOW_ALL); |
287 | spinlock_unlock(&rwl->lock); |
288 | spinlock_unlock(&rwl->lock); |
288 | interrupts_restore(ipl); |
289 | interrupts_restore(ipl); |
289 | } |
290 | } |
290 | 291 | ||
291 | 292 | ||
292 | /** Direct handoff of reader/writer lock ownership. |
293 | /** Direct handoff of reader/writer lock ownership. |
293 | * |
294 | * |
294 | * Direct handoff of reader/writer lock ownership |
295 | * Direct handoff of reader/writer lock ownership |
295 | * to waiting readers or a writer. |
296 | * to waiting readers or a writer. |
296 | * |
297 | * |
297 | * Must be called with rwl->lock locked. |
298 | * Must be called with rwl->lock locked. |
298 | * Must be called with interrupts_disable()'d. |
299 | * Must be called with interrupts_disable()'d. |
299 | * |
300 | * |
300 | * @param rwl Reader/Writer lock. |
301 | * @param rwl Reader/Writer lock. |
301 | * @param readers_only See the description below. |
302 | * @param readers_only See the description below. |
302 | * |
303 | * |
303 | * If readers_only is false: (unlock scenario) |
304 | * If readers_only is false: (unlock scenario) |
304 | * Let the first sleeper on 'exclusive' mutex in, no matter |
305 | * Let the first sleeper on 'exclusive' mutex in, no matter |
305 | * whether it is a reader or a writer. If there are more leading |
306 | * whether it is a reader or a writer. If there are more leading |
306 | * readers in line, let each of them in. |
307 | * readers in line, let each of them in. |
307 | * |
308 | * |
308 | * Otherwise: (timeout scenario) |
309 | * Otherwise: (timeout scenario) |
309 | * Let all leading readers in. |
310 | * Let all leading readers in. |
310 | */ |
311 | */ |
311 | void let_others_in(rwlock_t *rwl, int readers_only) |
312 | void let_others_in(rwlock_t *rwl, int readers_only) |
312 | { |
313 | { |
313 | rwlock_type_t type = RWLOCK_NONE; |
314 | rwlock_type_t type = RWLOCK_NONE; |
314 | thread_t *t = NULL; |
315 | thread_t *t = NULL; |
315 | bool one_more = true; |
316 | bool one_more = true; |
316 | 317 | ||
317 | spinlock_lock(&rwl->exclusive.sem.wq.lock); |
318 | spinlock_lock(&rwl->exclusive.sem.wq.lock); |
318 | 319 | ||
319 | if (!list_empty(&rwl->exclusive.sem.wq.head)) |
320 | if (!list_empty(&rwl->exclusive.sem.wq.head)) |
320 | t = list_get_instance(rwl->exclusive.sem.wq.head.next, thread_t, wq_link); |
321 | t = list_get_instance(rwl->exclusive.sem.wq.head.next, thread_t, wq_link); |
321 | do { |
322 | do { |
322 | if (t) { |
323 | if (t) { |
323 | spinlock_lock(&t->lock); |
324 | spinlock_lock(&t->lock); |
324 | type = t->rwlock_holder_type; |
325 | type = t->rwlock_holder_type; |
325 | spinlock_unlock(&t->lock); |
326 | spinlock_unlock(&t->lock); |
326 | } |
327 | } |
327 | 328 | ||
328 | /* |
329 | /* |
329 | * If readers_only is true, we wake all leading readers |
330 | * If readers_only is true, we wake all leading readers |
330 | * if and only if rwl is locked by another reader. |
331 | * if and only if rwl is locked by another reader. |
331 | * Assumption: readers_only ==> rwl->readers_in |
332 | * Assumption: readers_only ==> rwl->readers_in |
332 | */ |
333 | */ |
333 | if (readers_only && (type != RWLOCK_READER)) |
334 | if (readers_only && (type != RWLOCK_READER)) |
334 | break; |
335 | break; |
335 | 336 | ||
336 | 337 | ||
337 | if (type == RWLOCK_READER) { |
338 | if (type == RWLOCK_READER) { |
338 | /* |
339 | /* |
339 | * Waking up a reader. |
340 | * Waking up a reader. |
340 | * We are responsible for incrementing rwl->readers_in for it. |
341 | * We are responsible for incrementing rwl->readers_in for it. |
341 | */ |
342 | */ |
342 | rwl->readers_in++; |
343 | rwl->readers_in++; |
343 | } |
344 | } |
344 | 345 | ||
345 | /* |
346 | /* |
346 | * Only the last iteration through this loop can increment |
347 | * Only the last iteration through this loop can increment |
347 | * rwl->exclusive.sem.wq.missed_wakeup's. All preceeding |
348 | * rwl->exclusive.sem.wq.missed_wakeup's. All preceeding |
348 | * iterations will wake up a thread. |
349 | * iterations will wake up a thread. |
349 | */ |
350 | */ |
350 | /* We call the internal version of waitq_wakeup, which |
351 | /* We call the internal version of waitq_wakeup, which |
351 | * relies on the fact that the waitq is already locked. |
352 | * relies on the fact that the waitq is already locked. |
352 | */ |
353 | */ |
353 | _waitq_wakeup_unsafe(&rwl->exclusive.sem.wq, WAKEUP_FIRST); |
354 | _waitq_wakeup_unsafe(&rwl->exclusive.sem.wq, WAKEUP_FIRST); |
354 | 355 | ||
355 | t = NULL; |
356 | t = NULL; |
356 | if (!list_empty(&rwl->exclusive.sem.wq.head)) { |
357 | if (!list_empty(&rwl->exclusive.sem.wq.head)) { |
357 | t = list_get_instance(rwl->exclusive.sem.wq.head.next, thread_t, wq_link); |
358 | t = list_get_instance(rwl->exclusive.sem.wq.head.next, thread_t, wq_link); |
358 | if (t) { |
359 | if (t) { |
359 | spinlock_lock(&t->lock); |
360 | spinlock_lock(&t->lock); |
360 | if (t->rwlock_holder_type != RWLOCK_READER) |
361 | if (t->rwlock_holder_type != RWLOCK_READER) |
361 | one_more = false; |
362 | one_more = false; |
362 | spinlock_unlock(&t->lock); |
363 | spinlock_unlock(&t->lock); |
363 | } |
364 | } |
364 | } |
365 | } |
365 | } while ((type == RWLOCK_READER) && t && one_more); |
366 | } while ((type == RWLOCK_READER) && t && one_more); |
366 | 367 | ||
367 | spinlock_unlock(&rwl->exclusive.sem.wq.lock); |
368 | spinlock_unlock(&rwl->exclusive.sem.wq.lock); |
368 | } |
369 | } |
369 | 370 | ||
370 | /** Release spinlock callback |
371 | /** Release spinlock callback |
371 | * |
372 | * |
372 | * This is a callback function invoked from the scheduler. |
373 | * This is a callback function invoked from the scheduler. |
373 | * The callback is registered in _rwlock_read_lock_timeout(). |
374 | * The callback is registered in _rwlock_read_lock_timeout(). |
374 | * |
375 | * |
375 | * @param arg Spinlock. |
376 | * @param arg Spinlock. |
376 | */ |
377 | */ |
377 | void release_spinlock(void *arg) |
378 | void release_spinlock(void *arg) |
378 | { |
379 | { |
379 | spinlock_unlock((spinlock_t *) arg); |
380 | spinlock_unlock((spinlock_t *) arg); |
380 | } |
381 | } |
381 | 382 |